Fix the corner case when there is only "\0\0" appended and the Index is 1. Return missing string instead of empty string.
Fix the corner case when there is only "\0\0" appended and the Index is 1. Return missing string instead of empty string.

git-svn-id: 5648d1bec6962b0a6d1d1b40eba8cf5cdb62da3d@10914 6f19259b-4bc3-4df7-8a09-765794883524

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2